CN102509357A - Pencil sketch simulating and drawing system based on brush stroke - Google Patents
Pencil sketch simulating and drawing system based on brush stroke Download PDFInfo
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Abstract
The invention discloses a pencil sketch simulating and drawing system based on brush stroke. In the system, a three-dimensional geometrical model is used as input, and a pencil sketch picture is generated by combining automatic generation and interaction. The system classifies the brush strokes in the pencil sketch drawing into feature brush strokes and hatch brush strokes, and performs simulation and drawing respectively. The system mainly comprises a user interaction module, a feature path automatic generation module, a hatch path automatic generation module, a module for generating brush strokes from paths and a drawing output module. The system disclosed by the invention conforms to the actual pencil sketch creation mechanism of the human, realizes a real drawing effect, is easy to edit and modify and the like, and has important application values in the aspects of computer-aided design, artistic design, special effects, digital entertainment and the like.
Description
Technical field
The invention belongs to the cross discipline technical field that computer graphics, computer-aided design (CAD) and Artistic Design combine, relate to a kind of according to the perhaps interactive automatically method that generates based on the pencil sketch of style of writing of input 3-D geometric model.
Background technology
The analog simulation of various artistic medium is made and neighborhood such as Digital Image Processing values that has a wide range of applications in digital art design, digital entertainment, Film Animation always, and pencil sketch drawing has received extensive concern especially as the basic content of painting.Existing pencil sketch simulation method for drafting can be divided into four types substantially: based on the method for volume drawing, based on the method for texture, based on the method for image with based on the method for style of writing.
The work of very early time is the volume drawing model that people such as Takagi sets up in the pencil sketch simulation drawing.Object plotting method needs high storage capacities and calculated amount usually, and can only be used for the simulation of pencil drawing material.
Method based on texture generates some pencil sketch textures usually in advance, and the texture that generates is attached to the solid surface according to curvature direction.Because graphic hardware equipment is better to the texture support at present, this method can realize the real-time rendering of pencil sketch on three-dimensional geometry.The shortcoming of texture mapping method is because this method is only described object in the three dimensional object space, do not have the two dimensional image spatial information, thereby the result to be too regular, lacks the Freehandhand-drawing effect.
Based on the simulation of the pencil sketch of image all with two-dimensional digital image as input, at first according to input picture generted noise image and bivector field, use the final pencil sketch picture of line integral convolution (LIC) generation then.Opposite with texture mapping method, these class methods are only described rendered object in the two dimensional image space, can't utilize the three-dimensional geological information of object.Owing to lack structural information, data representation is generally comparatively loose, is unfavorable for editor.
All pencil sketch lines are treated as aggregate (texture or image) based on the method for texture with based on the method for image, lacked independent pencil line information, thereby can not reflect human painting process and drawing custom.Pencil sketch simulation method for drafting based on style of writing has then overcome above-mentioned shortcoming.Style of writing (strokes) has the geometric description of oneself, and each bar style of writing is corresponding to one in the drawing.Can also store various attributes in the style of writing, the pressure that uses when for example painting, color etc., this is to relate to that simulation is drawn and mutual application provides convenience.The user also can through pick up, edit, operation such as deletion changes style of writing.Full detail when the picture that is made up of style of writing has almost been preserved drawing.Because style of writing has geometry, can drawing result be exported with arbitrary accuracy in addition.The feasible method based on style of writing of these advantages has very high practicality, extensively is used in the various Artistic Design softwares.
Summary of the invention
The objective of the invention is to; (file layout has .obj to the various commercial 3-D geometric model storehouse that exists at present extensively or free 3-D geometric model file; .max; .3ds etc.), provide one based on system style of writing, that can generate pencil sketch drawing from the full-automatic perhaps interactive mode of input 3-D geometric model.The pencil sketch drawing that this system generates is made up of style of writing (stroke), can reflect the creation mechanism and the process of true pencil sketch, and be easy to edited and revise by the user, can be used for the virtual creation of various pencil sketch drawing.
The present invention proposes a kind of simulation of pencil sketch and drawing system based on style of writing, and this system comprises five modules:
User interactive module, being used to the user provides the interface to carry out that 3-D geometric model is selected and export the 3-D geometric model of selecting to characteristic path automatically-generating module and hachure path automatically-generating module;
Characteristic path automatically-generating module is used for the automatic generating feature of the 3-D geometric model path according to input;
Hachure path automatically-generating module is used for generating the hachure path automatically according to the 3-D geometric model of input;
Generate the style of writing module by the path, be used for according to the characteristic path of characteristic path automatically-generating module generation and the hachure path of hachure path automatically-generating module generation, the geometry and the attribute thereof of generating feature style of writing and hachure style of writing;
Draw output module, be used for geometry and attribute, adopt the pencil physical model to draw out the pencil style of writing according to style of writing.
The invention has the beneficial effects as follows to have proposed a kind of simulation of pencil sketch and drawing system,, utilize full-automatic generating algorithm or interactive tools to generate pencil sketch drawing according to the 3-D geometric model of input based on style of writing.The difference of the present invention and forefathers' method is mainly reflected in; Can generate a greater variety of characteristic styles of writing; And proposed a kind ofly to utilize sampling algorithm, automatically generate the new method of hachure style of writing, a kind of interactive tools of utilizing hachure frame (hatching carrier) to carry out the style of writing design is provided in addition.The user can also utilize interactive tools that system provides that the characteristic style of writing and the hachure style of writing of automatic generation carried out edit-modify or deletion action, also can add new characteristic style of writing and hachure style of writing.Can find out the pencil sketch paint that system can generate fast truly, have the Freehandhand-drawing effect from the pencil sketch result of final generation.Because system has the Aided Design effect, has reduced user's painting skill requirement, and has accelerated the creation speed of pencil sketch work.In addition since digital virtual design create with respect to the tradition of unusable paper and pencil, transmit, duplicate, aspect such as preservation has advantage, thereby this system has very high using value in fields such as digital art design, Film Animation special efficacy, digital entertainments.
Description of drawings
Fig. 1 is the modularization process flow diagram of system of the present invention.
Fig. 2 is the synoptic diagram by the path of tri patch extraction.
Fig. 3 is the process flow diagram that generates pencil hachure style of writing automatically.
Fig. 4 is the sampling algorithm process flow diagram based on cumulative probability density.
Fig. 5 is the sampling algorithm process flow diagram based on Metropolis-Hastings.
Fig. 6 is the synoptic diagram of two kinds of sampled point correction strategies.
Fig. 7 is sampled point correction effect figure.
Fig. 8 is the teapot pencil sketch effect figure that is generated automatically by system.
Fig. 9 is the plant pencil sketch effect figure that is generated automatically by system.
Figure 10 is the synoptic diagram by the path configuration style of writing.
Figure 11 is the synoptic diagram of the different written shapes in structure path.
The synoptic diagram of the interactive style of writing design tool that Figure 12 provides for system.
Figure 13 is the example of the movement locus of control particle in the interactive style of writing design tool.
The example of Figure 14 for using interactive style of writing design tool on reference picture, to draw the hachure style of writing.
Figure 15 is the example of the various styles of writing of interactive style of writing design tool drafting.
Figure 16 is the design sketch of interactive each step of pencil sketch design.
Figure 17 is the interactive plant pencil sketch effect figure that generates.
The colored pencil sketch effect figure of Figure 18 for drawing.
Embodiment
For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.
Fig. 1 has provided the modularization process flow diagram of total system.Total system mainly comprises five modules: user interactive module, characteristic path automatically-generating module, hachure path automatically-generating module, generated the style of writing module, drawn output module by the path.Wherein characteristic path automatically-generating module, hachure path automatically-generating module, generate the style of writing module, draw output module and control automatically by the path by system, user interactive module mainly provides various interactive tools to supply users to use.
System is at first by characteristic path automatically-generating module and automatically-generating module generating feature path, hachure path and hachure path, and the characteristic path of output and hachure path get into by the path as input and generate the style of writing module then.Generate the style of writing module according to the style of writing formation rule by the path,, and export the drafting output module to by characteristic path and how much of the hachure path generation styles of writing and the attribute of input.Draw style of writing how much and the attribute of output module at last according to input, and the physical model of pencil drafting, final pencil sketch picture generated.User interactive module provides interactive tools to whole generative process, makes the user to replenish the result of automatic generation, to delete and edit.
In instructions of the present invention, path (path) be meant style of writing the track of process.This track forms the trunk of style of writing, corresponding to the central point of brush tip in the actual handwritten drawings track of process on paper.Style of writing (stroke) is meant a kind of diagrammatic representation with geometric configuration and attribute in the computer graphics, corresponding to a certain lines in the actual handwritten drawings.Characteristic path (feature path) is meant the lines path that is used for describing characteristic, is commonly used to reflect the geometrical property (for example object boundary) of object, the border of color, the border of bright and dark light etc.Hachure path (hatching path) mainly is used for shadow, tone, color, material etc. in the represent scenes, and colony's set form of generally forming with a large amount of paths occurs.The style of writing that characteristic path and hachure path generate is called characteristic style of writing (feature stroke) and hachure style of writing (hatching stroke) respectively.
Reference picture (reference image) is a kind of technology that writes down and reflect three-dimensional information in the graphics with the 2-D data structure, is proposed by people such as Kowalski as far back as 1999.Internal memory just can be handled because the data of storing in the early stage frame buffer need be read back, and is stored as picture format usually, so be called reference picture.Along with the development of programmable graphics pipeline (programmable graphics pipeline), data can directly be handled in video memory at present, thereby also can be called with reference to buffer memory (reference buffer).
Can use three kinds among the present invention with reference to image, be respectively identity reference picture (ID reference image), color reference image (color reference image) and illumination reference picture (illumination reference image).Wherein the identity reference picture uses the different colours value to distinguish rendered object, is used for the blanking line algorithm of characteristic fragment; Color reference image and illumination reference picture are used for assisting and carry out the design of hachure.
Below in conjunction with 1 pair of user interactive module of accompanying drawing, characteristic path automatically-generating module, hachure path automatically-generating module, generate the style of writing module, draw output module and describe one by one by the path.
1. user interactive module
User interactive module provides following several tools to supply the user to carry out parameter and selects and interactive design:
(1) selected required 3-D geometric model is exported to characteristic path automatically-generating module and hachure path automatically-generating module, and on this basis, and model coordinate, camera coordinates, light source position and type, models etc. are selected and set.The user can also select the characteristic path type of generation automatically as required;
(2) after system drew out the color reference image according to selected geometric model and illumination model, the user can edit the color reference image as required;
(3) user can use the path design instrument directly to design in the basic enterprising walking along the street of reference picture as required, the description in the interactive tools of concrete reference path design;
(4) system provides dissimilar pencil types, is divided into 9B, 8B ... 2B, B, F, HB, H, 2H ... 6H etc., different pencil types, the number percent of its graphitiferous, earth, paraffin is also different;
(5) system adopts the Perlin noise to generate the height field of various paper, and can be used for the physical model that pencil is drawn;
(6) after automatic generating feature style of writing of system and hachure style of writing, the user can also use interactive tools to the style of writing that generates pick up, operations such as edit-modify, deletion, also can use interactive tools to add new style of writing.
2. characteristic path automatically-generating module
The function of characteristic path automatically-generating module is from the 3-D geometric model of input, to generate required characteristic path, mainly comprises following four steps:
(1) tri patch of from the 3-D geometric model of input, storing extracts characteristic fragment;
(2) according to the 3-D geometric model and the middle characteristic fragment structure identity reference picture that extracts of step (1) of input, be used for follow-up blanking line algorithm;
(3) utilize the identity reference picture, use the blanking line algorithm that characteristic fragment is carried out blanking;
(4) characteristic fragment after the blanking is linked into the characteristic path.
There are outline line (silhouettes or occluding contours), prompting outline line (suggestive contours), crease line (creases), boundary line (borders orboundary edges), crestal line (ridges), valley line (valleys), obvious crestal line (apparent ridges), prompting high light line (suggestive highlights), main high light line (principal highlights) etc. in the characteristic path of using in the system.These characteristic paths can be realized generating automatically from 3-D geometric model by existing method.The branch that does not have quality between the various characteristics path, all there is its unique characteristic in every kind of characteristic path, and also all there are suitable and inapplicable occasion in every kind of characteristic path.Exist between some characteristic path and overlap and similar composition; For example crestal line and obviously crestal line, obvious crestal line and prompting outline line, therefore, in actual use; The kind in characteristic path neither be The more the better; The chaotic that seems easily too much, and the required characteristic of the not enough very little reflection in characteristic path have reduced final pencil sketch result's performing content.Therefore the present invention both provided the module in automatic generating feature path, also in user interactive module, provided instrument to allow the user to add paths voluntarily.In actual the use; At first let system automatic generating feature path and hachure path as required by the user; Then the user according to the result of automatic generation select, editor, deletion action, perhaps adding new characteristic path and hachure path voluntarily is more convenient effective solution.
Existing is that the characteristic path extraction method of importing is all obtained the characteristic path with the 3-D geometric model from the calculating of tri patch.The characteristic path of extracting in the single tri patch is called a characteristic fragment (feature segment), and it is made up of the line of two end points and two end points.End to end a plurality of characteristic curve fragment links formation characteristic path.Here be that example describes with the outline line, the characteristic path extraction algorithm of other type can be with reference to corresponding document.
For smooth surface, outline line can be defined as from mathematics:
n
i·(c-v
i)＝0，
Wherein, v
iBe the volume coordinate of summit i, n
iBe v
iVertex scheme vector, c is the volume coordinate of camera.Specific algorithm is following in the practical application: at first standardization dot product value is calculated on each summit in the tri patch:
Then according to following formula mark summit symbol:
If the s on three summits in the tri patch
iValue occur contrary sign situation (2 for+number 1 for-number, perhaps 2 be-number 1 and be+number), then explain to have characteristic fragment in this tri patch, shown in Fig. 2 (a).Promptly can obtain two end points (s of characteristic fragment with following linear interpolation formula
1, s
2):
Because curved surface is continuously smooth, so the characteristic fragment that extracts in each tri patch can join end to end naturally and form the characteristic path, shown in Fig. 2 (b).
Among the present invention, after characteristic fragment extracted, the expression in characteristic path was the set of series of features fragment at present.Reason owing to depth occlusion; Wherein many fragments are sightless; But characteristic fragment extracts the information of the former 3-D geometric model face in back not to be existed, and when drawing these characteristic fragments, the z-buffer in the graphic process unit only can carry out depth detection on fragment pixel; The characteristic fragment of drawing out can not reflect the depth information of former three-dimensional geometry, therefore needs to use the blanking line algorithm to realize the characteristic fragment blanking.Used herein is to utilize the identity reference picture to carry out the algorithm of blanking.This algorithm is proposed in 2000 by people such as Northrup, is a kind of geometry and image blend efficient rendering algorithm.This algorithm is at first constructed identity reference picture (ID reference image): with characteristic fragment and 3-D geometric model with the different colours mark and be plotted to frame buffer zone (frame buffer), then with drawing result from the frame buffer zone internal memory structure identity reference picture that reads back.When carrying out the characteristic fragment blanking, some specified pixel in each characteristic fragment and the identity reference picture is detected coupling realize blanking.
After the characteristic fragment set of extracting carried out blanking, ensuing work was the fragment after these blankings to be joined end to end form the characteristic path, so that follow-up generation style of writing is drawn for how much.If some characteristic fragment length is too short, on screen,, can these fragments and adjacent fragment be merged less than a pixel.
If the path that generates is long; Do not meet actual drawing style; Can long path be divided into some short paths according to MAXPATHLEN, perhaps according to the angle between the adjacent segment in the path, the place that bend ratio is bigger in the path is cut apart the path.
3. hachure path automatically-generating module
The function of hachure path automatically-generating module is from the 3-D geometric model of input, to generate required hachure path, mainly comprises following three steps:
(1) draw out corresponding color reference image and illumination reference picture according to the 3-D geometric model of input, specifically generating which kind of reference picture can be decided by illumination and coloring models;
(2) user can use the color edit tool that the color reference image is edited as required;
(3) generate the hachure path by color reference image and illumination reference picture.The user also can utilize interactive tools that user interactive module provides in the enterprising edlin of result and the modification that generate automatically afterwards.
Hachure in the pencil sketch is the set that a series of styles of writing are arranged by certain rule.The hachure style of writing can be expressed information such as illumination, color, material, shape simultaneously through tone (tone).Style of writing has two attributes: 1, color harmony texture, the i.e. attribute of wall scroll style of writing can be explained simultaneously in each bar style of writing.2, the set of many styles of writing also can reflect the color harmony texture, i.e. the group property of style of writing.
In our system, can design hachure according to color reference image and illumination reference picture respectively.They correspond respectively to the build-in attribute (intrinsic property) and the external attribute (extrinsic property) of object.Distinguish build-in attribute and external attribute these two parts can independently be edited, for example independent color software for editing or the illumination software for editing of using.Another even more important reason is; Mix build-in attribute and external attribute and usually can cause visual mismatch; Even this point all is difficult to hold for professional painter; Because the user can well estimate the color that object is original, but the illumination color that reflects on the very difficult correct estimation object.Color system and illumination system differentiation are treated, with color reference image and illumination reference picture location tone, will well be avoided this vision mismatch respectively.The user comes the original color of specified object, and existing lighting drawing system can quantize light intensity in the graphics, so just can realize sharing out the work and help one another of user and computing machine.In fact, the method for designing of differentiation build-in attribute and external attribute also has record in professional art teaching skill and technique.From the difference of professional background, computerite and art worker are at term and describe difference to some extent, but theory is identical with essence.For example Dodson has recorded and narrated how to understand the painting creation process from the angle of this tone, shadow pattern, lightness pattern in its classical drawing study course " Keys to Drawing ": the painter combines shadow pattern and this tone, just can obtain the lightness pattern of finally drawing a picture according to photo.Differentiation color reference image and illumination reference picture also are based on this painting creation theory in the system.
The main attribute of single hachure has position, direction, length, pressure distribution etc., and the hachure set also has group properties such as density in addition.In actual painting process, the painter is constantly observing on the basis of object, with style of writing being arranged on the drawing paper stroke by stroke, finally approaches the drawing object with all styles of writing on the drawing paper.This process can abstractly be a sampling problem, and we represent that with reference picture then the generation of hachure and distribution problem can be regarded the sampling problem of a two-dimentional reference picture as at the object of will painting.
During concrete the realization, can be step by step the various attributes of photographic fixing line really, whole hachure style of writing generative process is with reference to figure 3.Below for the hachure style of writing generates step, wherein step (1)-(4) generate step for the hachure path:
(1) at first draws out reference picture (Fig. 3 (b)) according to the 3-D geometric model (Fig. 3 (a)) of input;
(2) use certain method of sampling to obtain the position and the distribution (Fig. 3 (c)) of hachure according to reference picture then, the concrete method of sampling will be narrated below;
(3) because style of writing has size and shape, consider that the coincidence of sampled point can exert an influence to drawing effect, also need revise (Fig. 3 (d)) to sampled point;
(4) after the sampled point correction; Confirm the hachure path direction according to the gradient information of reference picture again; Then confirm the hachure path according to the gray-scale value of reference picture; Confirm the hachure path shape through the Bezier interpolation then, confirm hachure pressure distribution (Fig. 3 (e)) at last, so far the hachure path generates;
(5) the final hachure path that generates generates the hachure style of writing through generating the style of writing module by the path, and draws out net result (Fig. 3 (f)) by drawing output module.
The two-dimensional probability density function of hypothetical reference image is that (x, y), then hachure design is equivalent to that (x obtain some sampled points in y) and generate style of writing, and the style of writing of these generations can be used for reflecting the distribution character of former reference picture from f to f.Here we inquire into two kinds of sample modes: based on the sampling of cumulative probability density with based on the sampling of Metropolis-Hastings algorithm.
Sampling based on cumulative probability density is exactly to utilize the slope of cumulative probability density function that equally distributed random number is redistributed, and its one dimension algorithm is as shown in Figure 4.This algorithm is at first according to probability density function calculating cumulative probability density function; Generate equally distributed random vector then; And utilize the inverse function of cumulative probability density function that equally distributed random vector is carried out conversion, then the random vector after the conversion meets initial probability density function profiles.(x y), can ask for marginal probability density function to y earlier, uses above-mentioned one dimension cumulative probability density algorithm then, obtains the distribution of x according to condition probability formula again and uses above-mentioned one dimension cumulative probability density algorithm for two-dimensional probability density function f.Its way is actually through marginal probability density and conditional probability density, is earlier y to be sampled with two-dimentional sample conversion, and then x is sampled.
The Metropolis-Hastings algorithm is a kind of algorithm that can sample to any complex distributions.This algorithm only need know the probability estimate value of treating sampled point or treat the probability estimate ratio between the sampled point, just can sample not knowing under the situation of probability distribution function, has good universality.For two-dimensional digital image; Adopt this algorithm can be directly to carry out the two dimension sampling as estimated value, avoided in the cumulative probability density sampling algorithm estimation for probability density function, marginal probability density function, conditional probability density function with the gray-scale value of image.Suppose that we need N sampled point, (the probability estimate value does the two-dimentional sampled point on the image for x, y) expression with z=
Current sampled point is z
n, generate candidate's sampled point z
*Proposal be distributed as Q (z
*| z
n), the Metropolis-Hastings algorithm that then generates N sampled point is as shown in Figure 5.When algorithm begins the sampled point number n that generates is initialized as 0.When the sampled point number that generates during less than N, the algorithm circulation is carried out, otherwise algorithm finishes.The interior algorithm of each circulation generates candidate's sampled point according to proposing to distribute, and calculates its acceptance probability, and compares with a random number, thereby determines whether candidate's sampled point of this generation should be accepted.The Metropolis-Hastings algorithm is at every turn according to current sampling point z
nGenerate next sampled point, its sampled point sequence (z
1, z
2..., z
n) form a Markov chain, and the sequence path is the random walk of two dimensional surface.Algorithm confirms to accept A (z
n→ z
*The sampled point of)>=1 is accepted A (z at random
n→ z
*The sampled point of)＜1.Along with the increase of sampled point number N, the distribution of sampled point sequence can level off to probability density function f (x, y).
In the pencil sketch simulation application of the present invention, sampled point is used for reflecting that style of writing distributes, and style of writing has area because sampling is what in limited reference picture zone, to carry out, must have between some sampled point the position near in addition overlapping.See that from the visual effect of final drafting the close sampled point in position shows as a series of overlapping styles of writing, thereby weaken the visual effect of drafting.More obvious under the situation such as this is lower in the style of writing transparency, style of writing lacks Overlay.The mean pixel number of style of writing is many more in the final generation picture, and then the overlapping influence that causes of sampling point position also can be big more.Though see from statistic histogram, the distribution of sampled point has approached required probability distribution really, and actual the drafting on the effect do not reach requirement.
To the problems referred to above, the present invention carries out correction among a small circle to the sampled point that obtains.The overlapping correction algorithm of concrete sampled point is following:
(1) each sampled point z to obtaining
n, search whether there is other sampled point in its neighborhood, wherein the minimum sampled point spacing of the radius of neighborhood for tolerating can be set at the half the of average style of writing width;
(2) if having other sampled point in the neighborhood, then calculate the place-centric of other sampled point, let the sampled point z that is investigated then
nMove along the direction opposite with other sampling point position center a bit of apart from δ, shown in Fig. 6 (a).In order not influence the probability distribution of the sampled point that obtains, we only let sampled point move to the target location that has a same gray-scale value with its origin-location.
(3) whether the inspection target location meets the demands, if the target location does not meet the demands, then lets sampled point z
nMove along reverse direction from its nearest sampled point a bit of apart from δ, shown in Fig. 6 (b);
(4) if the gray-scale value of target location does not still meet the demands, then abandon revising sampled point z
n, reach the effect of avoiding overlapping by the correction of other sampled point;
(5) above-mentioned makeover process can iterate and carry out several times, till most sampled points all meet the demands.
Use the overlapping correction algorithm of sampled point can reach better drafting effect, the maximized drafting effect of utilizing each bar sampled point to generate style of writing with the least possible sampled point.
Fig. 7 (c) and Fig. 7 (d) have showed the overlapping design sketch of revising front and back of sampled point respectively.Input 3-D geometric model that it is corresponding and reference picture are respectively shown in Fig. 7 (a) and Fig. 7 (b).Can find out that the overlapping correction algorithm of sampled point that the present invention proposes can make sampled point avoid overlapping as far as possible, promote the visual effect that single sampled point generates style of writing.
After obtaining the information of hachure position and distribution, then can confirm the hachure direction according to the reference picture gradient information.In order to keep generating the characteristic style of writing information in the picture, the direction that system adopts and image gradient is perpendicular can also make style of writing size and shape that the influence of sampling is reached minimum as the hachure direction like this.If the gradient of reference picture is less than a certain threshold value, then with the default direction of " down left-upper right " direction as hachure, this direction is the most frequent direction of human Freehandhand-drawing hachure, also meets most human drawing custom and ergonomic features.Because the painter often uses the pictorial skill (hand does not stop to draw a picture in the time of the eye gaze rendered object) of " blind picture " in the painting process; And nib is jumped through regular meeting, thereby this default direction all has certain scientific basis aspect theoretical and the experiment.
After confirming hachure position, distribution and direction, hachure length and path can be obtained by following algorithm:
1, generates the control particle: on the sampled point of each generation, generate pair of control particle [p
+, p
-], the control particle has speed (v
x, v
y) and priming color c
0Deng attribute.Wherein every pair of control particle's velocity direction is consistent in the other direction with hachure direction and hachure respectively;
2, move the control particle: calculate the target location of each control particle, promptly control particle along speed (v
x, v
y) direction moves the position of a step-length, step-length can be set as required, is generally 1 to 5 pixel value; If the reference picture gray-scale value c of control particle target location
pSatisfy | c
0-c
p|＜δ
c, then let the control particle move to the target location; Reach maximum style of writing length if do not satisfy or control particle, then let the control particle stop; δ wherein
cBe a threshold value, δ
cBig more, then the soft edges effect of hachure style of writing is more for obvious; δ
cMore little, the hard edge effect of hachure style of writing is more for obvious;
3, according to every pair of final position of control particle, adopt the Bezier interpolation method to obtain the hachure path.Also can write down the pressure distribution of corresponding hachure style of writing in the hachure path according to the gray-scale value of reference picture, draw to be used for follow-up pencil style of writing.
From overlapping correction algorithm of sampled point and hachure path generating algorithm, can find out; We let each bar hachure region covered have approximate gray scale all the time; Promptly according to the hachure that distributes of the color lump in the image; This meets in the study course of pencil sketch specialty and decomposes the theory of painting according to shape, thereby can make the pencil sketch picture of generation have Freehandhand-drawing effect preferably.
Fig. 8 (c) has showed that the propelling pencil sketch of teapot geometry generates the result, and wherein characteristic style of writing and hachure style of writing generate by algorithm automatically.Have 38 characteristic styles of writing and 8000 hachure styles of writing among the figure.Fig. 8 (a) and Fig. 8 (b) have then showed the 3-D geometric model and the illumination reference picture of drawing generation of input respectively.
Fig. 9 (c) has showed the pencil sketch picture that another width of cloth generates automatically, has wherein comprised 266 characteristic styles of writing and 8000 hachure styles of writing of automatic generation, and corresponding 3-D geometric model input and illumination reference picture are respectively shown in Fig. 9 (a) and Fig. 9 (b).
4. generate the style of writing module by the path
The function of this module is by characteristic path or hachure path generating feature style of writing or hachure style of writing.Referring to Figure 10, the path represented by square summit and dotted line, representative be the track of nib process; Style of writing represented by rounded vertex and solid line, representative be lines shape and the texture that nib stays on paper.Mentioned in the content of last branch, style of writing has two attributes: 1, color harmony texture (independent attribute) can be explained simultaneously in each bar style of writing.2, the set of many styles of writing also can reflect color harmony texture (attribute of colony).This part content relates generally to the characteristic of wall scroll style of writing, and the group property of style of writing had been narrated in the automatically-generating module of hachure path.
Characteristic path and hachure path that characteristic style of writing in the system and hachure style of writing are obtained by aforementioned two modules respectively, and the common generation of pencil nib shape (tip shape), shown in figure 10.Wherein square vertex representation forms the summit in path, and it and path line segment have formed the geometric representation in path jointly; Rounded vertex and solid line line segment have been formed how much of style of writing.The nib shape positions the geometric configuration of style of writing at each path vertices place, thereby has formed how much of style of writing together with the path.The nib shape is made up of a series of predefined shapes, and for example typical case's (typical) shape, wide head (broad) shape, chisel (chisel) shape etc. are shown in figure 11.Nib also has a series of size to select for the user.For the characteristic path, we also can use the details of input geometry to come to regulate automatically the size of nib, because the user uses thinner nib to keep details usually at the details place.The influence that nib also can be under pressure in the drawing, pressure is big more, and the written size that pencil forms on paper also can be big more.Therefore final written big or small S can represent with following formula:
S＝s
t×f
g×f
p，
Wherein, s
tBe the overall written size that the user selects, f
pBe press factors, f
gBe the geometric detail zoom factor, can use following formula definition:
Wherein, A
vBe the leg-of-mutton Voronoi area of ring (one-ring Voronoi area) on input geometric model summit,
Be controlling elements.
5. drafting output module
The function of this module is to be depicted as final pencil effect picture by style of writing.Draw the pencil physical model that uses and adopt Sousa pencil model, and in GPU (GPU), realize respective algorithms.GPU is the arithmetic element of modern video card, and different with CPU is that the parallel processing capability of GPU is very powerful, is fit to handle the magnanimity graph data.
Sousa pencil model has related to pencil and the paper a plurality of physical descriptors when mutual, and is that base unit is simulated with the grain (grain) in how much on the paper.Each grain is made up of four adjacent in paper height field centrums that highly surround.System deposits (comprising graphite, earth and paraffin) height of paper and the composition of pencil-lead the R of texture in respectively, G, and B in the A channel, and is packaged into two buffer memorys.During drafting, exchange two textures iteratively and upgrade each component in the texture as render target and according to the pixel coloring process.Content according to graphite, earth and the paraffin of storage in the texture pixel (the corresponding grain of each pixel) generates final pencil effect picture at last.For example, if the color of graphite is C
G, the color of earth is C
C, the color of paraffin is C
V, graphite, earth and the paraffin content in certain grain is respectively V
G, V
CAnd V
V, the color value C that then final this grain shows is:
C＝C
G×V
G+C
C×V
C+C
V×V
V，
The color value that all grains show on the paper has reflected the color value of final pencil sketch picture jointly, forms the drafting effect of pencil sketch.The user also can carry out edit-modify to final style of writing, draws again then.Because the render speed of GPU is very fast, can satisfy the requirement of real-time, interactive basically.
6. the interactive tools of hachure design
System provides the instrument of several kinds of Batch Design hachures on reference picture; They are parallel curves hachure instrument (parallel curve hatching tool), wave hachure instrument (wave hatching tool), cross hatch instrument (cross hatching tool) and free hachure instrument (free hatching tool), and are shown in figure 12.Wherein parallel curves hachure instrument has parameter and can control its degree of crook and symmetry.Wave hachure instrument provides parameter to control the level and smooth degree of its wave.Through parameter regulation, the parallel curves hachure can be degenerated to parallel lines hachure (parallel line hatching), and the wave hachure can be degenerated to sawtooth hachure (zigzag hatching).The hachure of these kinds all is the common hachure in the pencil sketch drawing.System also provides free hachure instrument to supply the user to design the hachure of own demand pattern.Because free hachure instrument can draw the style of writing of any pattern, thereby not only can be used for designing the path of hachure style of writing, also can be used for the path of design feature style of writing.The characteristic style of writing of design and hachure style of writing promptly obtain required characteristic style of writing and hachure style of writing through generating the style of writing module by the path.We use the notion of hachure frame (hatching carrier) to be used as the carrier of style of writing path design instrument; As among Figure 12 from left to right and shown in the longest path; Said hachure frame is the independent paths that the user drew, and the hachure path is carried out in batches, generated automatically according to the path of hachure frame.In painting process, the user only need use interaction type input apparatus, and for example mouse, pen force etc. are drawn out the style of writing frame on reference picture, and the hachure instrument will be drawn out a series of hachures that can reflect local tone according to region shape automatically.The staff curve plotting is simple and flexible, can just can accomplish the hachure design in a zone according to a hachure frame, thereby can reach the purpose of quick design hachure, is similar to the gesture identification in the browser.
The specific algorithm that generates hachure with the hachure frame in batches is following:
When (1) user draws the hachure frame, note the coordinate point sequence of input and the reference picture pixel value of process, and calculate the median pixel value c of the reference picture pixel of process
m
(2) some control particle p of initialization on the hachure frame
1, p
2... p
i, p
j... p
n, these control particles have speed (v
x, v
y) and priming color c
0Deng attribute, priming color c wherein
0By the reference picture color value decision of control particle position, initial velocity is set according to the type of hachure.When specifying the priming color value of certain control particle, represent jointly below, for example control particle P with control particle sequence number and 0
iThe priming color value be c
I0, use c when making a general reference certain control particle color value
0Expression.Control particle p
iAnd p
jBetween spacing do
δ wherein
dBeing the density controlled variable, is unit with the pixel.Here suppose all colours value c
m, c
0, c
I0, c
J0Standardized to [0,1] Deng all;
(3) system let the control particle according to the type of hachure to two lateral movements of hachure frame, shown in the white arrow among Figure 13, the white fine rule among the figure has shown the motion path of control particle.Here only let the control particle satisfy | c
0-c
m|＜δ
cRegion memory live, the control particle leaves this zone will be dead (implication of discussing in dead here implication and the particIe system is consistent, i.e. the release of the termination of particle function and storage space).δ wherein
cBe the color distortion controlled variable in the zone, can regulate by the user.δ
cBig more, the soft edges effect of then drawing out is obvious more; δ
cMore little, the hard edge effect of then drawing out is obvious more:
(4) according to the dead position of control particle, obtain the hachure path with Bezier interpolation or Catmull-Rom interpolation.
Can find out the following several characteristics of having of this hachure design tool: the hachure type is specified by the user, and the hachure direction is specified (user's control) indirectly by the hachure frame.Color harmony hachure density is confirmed (computer control) automatically by color reference image and illumination reference picture.The shape of hachure design tool in can the perception reference picture, and can automatic distinguishing soft edges and hard edge (computer control).Figure 14 has showed the surface chart that uses hachure design interactive tools, on the basis of reference picture, designs hachure.
Figure 15 (b) has showed a secondary simple pencil literary sketch, and the 3-D geometric model of its input is shown in Figure 15 (a).This result has mainly showed the characteristic style of writing of automatic generation and the various hachure styles of writing (comprising parallel curves hachure, wave hachure and cross hatch) that interactive tools is drawn.291 characteristic styles of writing and 777 hachure styles of writing have been comprised among the figure altogether.As can be seen from the figure, the pencil lines of system's drafting are still relatively more real.Thickness, the pressure of lines all are full of variety, and are similar to people's Freehandhand-drawing effect.
The drawing process of all having showed cow pencil sketch among Fig. 1 and Figure 16 (a)-(d).What wherein Figure 16 (a) showed is the characteristic style of writing that generates automatically; Figure 16 (b) has showed according to the mutual hachure style of writing (build-in attribute is represented this tone) that generates of editor's color reference image; Figure 16 (c) has showed according to the mutual hachure style of writing (external attribute is represented the shadow pattern) that generates of illumination reference picture.All styles of writing are plotted in and have then formed final drafting effect together among Figure 16 (a), Figure 16 (b) and Figure 16 (c), shown in Figure 16 (d).211 characteristic styles of writing and 2747 hachure styles of writing have wherein been comprised altogether.As previously mentioned, this drafting mode is to meet human cognition of painting and custom.
Figure 17 (c) has showed the plant pencil sketch of the interactive tools generation that a secondary using system provides, and that shows among corresponding input 3-D geometric model and reference picture and Fig. 9 (a) and Fig. 9 (b) is identical, respectively shown in Figure 17 (a) and Figure 17 (b).266 characteristic styles of writing and 7231 hachure styles of writing have been comprised among Figure 17 (c) altogether.Can find out from the comparison of Figure 17 (c) and Fig. 9 (c); Automatically generation method and interactive method for designing all can generate real pencil sketch; But the result who is to use interactive tools to draw compares with the result of automatic generation, and it is better that detail section is handled, and also has more the Freehandhand-drawing effect.
Figure 18 has showed the colored pencil sketch that a width of cloth uses interactive tools to generate, and has comprised 766 characteristic styles of writing and 2631 hachure styles of writing altogether.Wherein the characteristic style of writing is generated by system automatically, and the hachure style of writing is generated by interactive tools.Color among Figure 18 is from the color reference image.Can find out that from the result pencil sketch picture that system generates is comparatively true and have an effect of manual drawing.
Because the system among the present invention is generating feature style of writing and hachure style of writing automatically; And allow the user that the style of writing that generates is edited and revised; Also can use interactive tools to add style of writing voluntarily; The interactive tools that system provides also can be according to the tone auto arrangement hachure in the reference picture, thereby has reduced user's professional painting skill requirement.In addition according to statistics, the hachure speed that the user of no foundation of painting uses interactive tools to draw is 5-11 style of writing/second, and this draws hachure speed faster than conventional artificial greatly.Use the advantage of interactive tools design hachure more outstanding when large tracts of land is drawn hachure, thereby native system is more suitable for the significantly drafting of works.In addition, system uses common mouse as input at present, if use instruments such as professional input pen and pressure handwriting pad, estimated efficiency also has further lifting.
Can find out that from top analysis system of the present invention can simulate pencil sketch work true to nature.Also can be following even there is not the user of foundation of painting assisting of system, generate pencil sketch work fast with Freehandhand-drawing effect.Because system is based on style of writing, with respect to pencil sketch generation methods such as other image, volume drawing, texture, has and meet actual painting creation process, be easy to advantage such as edit-modify, thereby have higher practical value.
Above-mentioned experimental result and based on simulation of the pencil sketch of style of writing and method for drafting; Can be used for fields such as computer graphics, computer-aided design (CAD), film animation special efficacy, Artistic Design, have simple to operate, formation speed is fast, effect is true to nature, be easy to revise and editor, characteristics that application prospect is wide.
Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (11)
1. the pencil sketch based on style of writing is simulated and drawing system, it is characterized in that this system comprises:
User interactive module, being used to the user provides the interface to carry out that 3-D geometric model is selected and export the 3-D geometric model of selecting to characteristic path automatically-generating module and hachure path automatically-generating module;
Characteristic path automatically-generating module is used for the automatic generating feature of the 3-D geometric model path according to input;
Hachure path automatically-generating module is used for generating the hachure path automatically according to the 3-D geometric model of input;
Generate the style of writing module by the path, be used for according to the characteristic path of characteristic path automatically-generating module generation and the hachure path of hachure path automatically-generating module generation, the geometry and the attribute thereof of generating feature style of writing and hachure style of writing;
Draw output module, be used for geometry and attribute, adopt the pencil physical model to draw out the pencil style of writing according to style of writing.
2. the system of claim 1; It is characterized in that said user interactive module also provides interactive tools to supply the user to carry out following operation: color reference picture editting, hachure path design, pencil attribute are chosen, the sketch paper selection of parameter, add the deletion style of writing and edit-modify has generated style of writing.
3. system as claimed in claim 2; It is characterized in that; Said hachure path design is meant that system's common hachure type in to the pencil sketch concludes on the basis of summary; It is divided into four types; And use parallel curves hachure instrument, wave hachure instrument, cross hatch instrument and free hachure instrument respectively, with hachure frame (hatching carrier) as carrier carry out interactive mode, the hachure path generates in batches, wherein free hachure instrument also can be used for the path of design feature style of writing.
4. system as claimed in claim 3 is characterized in that, said hachure frame is the independent paths that the user drew, and the hachure path is carried out in batches, generated automatically according to the path of hachure frame.
5. system as claimed in claim 3 is characterized in that, said with the hachure frame as carrier carry out interactive mode, in batches the step that generates of hachure comprises:
Step 1: when the user drew hachure frame path, system log (SYSLOG) descended the coordinate point sequence of input and the reference picture pixel value of process, and calculated the median pixel value c of the reference picture pixel of process
m
Step 2: system is some control particle p of initialization on the hachure frame
1, p
2... p
i, p
j... p
n, these control particles have speed v
x, v
yWith priming color c
0, and control particle p
iAnd p
jBetween spacing do
δ wherein
dBeing the density controlled variable, is unit with the pixel, c
I0Be control particle p
iThe priming color value, c
J0Be control particle p
jThe priming color value;
Step 3: system let the control particle according to the type of hachure to two lateral movements of hachure frame, and only let the control particle satisfy | c
0-c
m|＜δ
cRegion memory live δ wherein
cIt is the color distortion controlled variable in the zone;
Step 4: according to the dead position of control particle, with Bezier (B é zier curve) interpolation or Ka Temaer-obtain the hachure path like (Catmull-Rom) interpolation not.
6. the system of claim 1 is characterized in that, the step in said automatic generating feature path comprises:
(1) tri patch of from the 3-D geometric model of input, storing extracts characteristic fragment;
(2) construct the identity reference picture according to the 3-D geometric model and the middle characteristic fragment that extracts of step (1) of input;
(3) utilize the identity reference picture, use the blanking line algorithm that characteristic fragment is carried out blanking;
(4) characteristic fragment after the blanking is linked into the characteristic path.
7. the system of claim 1 is characterized in that, the step in said automatic generation hachure path comprises:
(1) draws out corresponding color reference image and illumination reference picture according to the 3-D geometric model of input;
The position and the distribution of (2) color reference image and illumination reference picture being sampled and obtaining hachure;
(3) sampled point is revised, to weaken the overlapping influence of style of writing to final drafting effect;
(4) sampled point is revised after, confirm the hachure path direction according to the gradient information of reference picture, confirm the hachure path according to gray-scale value, confirm the pressure distribution on the hachure path then, thereby generate the hachure path.
8. system as claimed in claim 7; It is characterized in that; Said color reference image and illumination reference picture correspond respectively to build-in attribute and the external attribute of drawing object, and its implication corresponds respectively to this color harmony shadow pattern of drawing object in the study course of specialty drawing.
9. system as claimed in claim 7 is characterized in that, the employed algorithm of said sampling have based on the sampling of cumulative probability density and based on the ultra Pohle of rice this-sampling of Haas spit of fland (Metropolis-Hastings) algorithm.
10. system as claimed in claim 7 is characterized in that, the said step that sampled point is revised comprises:
(1) each sampled point z to obtaining
n, search whether there is other sampled point in its neighborhood, wherein the minimum sampled point spacing of the radius of neighborhood for tolerating can be set at the half the of average style of writing width;
(2) if having other sampled point in the neighborhood, then calculate the place-centric of other sampled point, let the sampled point z that is investigated then
nMove a bit of along the direction opposite apart from δ with other sampling point position center;
(3) whether the inspection target location meets the demands, if the target location does not meet the demands, then lets sampled point z
nMove a bit of apart from δ along reverse direction from its nearest sampled point;
(4) if the gray-scale value of target location does not still meet the demands, then abandon revising sampled point z
n, avoid overlapping by the correction of other sampled point;
Iterate above-mentioned makeover process for several times, till most sampled points all meet the demands.
11. system as claimed in claim 10 is characterized in that, said target location can use following two kinds of methods to differentiate:
In order not influence the probability distribution of the sampled point that obtains, the requirement of target location is: the sampled point target location has same gray-scale value with its origin-location;
Perhaps in order to reduce the influence of correction algorithm to the sampled point probability distribution as far as possible, the requirement of target location is: the gray-scale value of sampled point target location differs certain threshold value with the gray-scale value of its origin-location.
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| CN109325986A (en) * | 2018-09-11 | 2019-02-12 | 广东智媒云图科技股份有限公司 | A kind of method for drafting and device of sketch |
| CN109300178A (en) * | 2018-09-11 | 2019-02-01 | 广东智媒云图科技股份有限公司 | A kind of souvenir figure generation system based on automatic sketch |
| CN113168723A (en) * | 2018-12-05 | 2021-07-23 | 索尼集团公司 | Repairing tool |
| CN113168723B (en) * | 2018-12-05 | 2024-05-28 | 索尼集团公司 | Repair tool |
| CN110453395A (en) * | 2019-07-19 | 2019-11-15 | 广东智媒云图科技股份有限公司 | A kind of intelligent robot embroidering method, electronic equipment, storage medium |
| CN110453395B (en) * | 2019-07-19 | 2021-04-09 | 广东智媒云图科技股份有限公司 | Intelligent robot embroidery method, electronic equipment and storage medium |
| CN111223184A (en) * | 2019-11-19 | 2020-06-02 | 中煤航测遥感集团有限公司 | Target curve drawing method and device |
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